1. Field of the Invention
This invention relates to a method of estimating planar flow from Doppler velocity distribution in an observation plane of a fluid, and more specifically relates to an improved planar flow estimation method that can display a flow velocity distribution as streamlines while utilizing a flow function by estimating an inflow/outflow flow rate of a boundary line or boundary surface.
2. Description of the Prior Art
A method to observe the flow velocity distribution of a fluid in an observation plane by using the Doppler effect of an ultrasonic wave is put to practical use, for example, in observing the rate of blood flow in the heart. Such a blood flow distribution is displayed in color on an ultrasonic wave tomogram of the heart, and is widely used in diagnosing bloodstream in the heart.
This Doppler velocity may be found using electromagnetic waves instead of ultrasonic waves. In recent years, it has been widely used to perform flow velocity observations in oceans, lakes or of cloud movements in the air.
Usually, a Doppler velocity distribution can measure only speed components in the transmitted and received wave directions of the observation beam, however it is necessary to estimate also the component in the direction perpendicular to the beam.
It was thought that the component in the orthogonal direction could be estimated by applying the concept of a stream function, but as blood flow in the heart and current or cloud flows are three dimensional, the estimation was not always satisfactory. Conventionally, surfaces that could be observed with beams are two-dimensional surfaces, this two-dimensional observation plane being obtained by linear or sector scanning with an ultrasonic wave beam or the like. However in a real fluid, there is inflow/outflow to and from the boundary line which is the side boundary of this two-dimensional observation plane. Similarly, there is also inflow/outflow to and from the boundary surface which is a boundary between the observed two-dimensional observation plane and the adjacent (three-dimensional) layer.
Therefore, using conventional methods which take no account of inflow/outflow of fluids on boundary surfaces, there was a problem in that observation and estimation of planar flow in real fluids could not be made.